Oil on spark plugs

Ive been having some issues lately with my í99 Protege, lacking power, and I feel sudden dips when traveling down the highway. Pulled the plugs today to find oil on three of the four. There is some oil ON the plug, but I believe that there is also oil in the chamber. How can I be sure, and what is the fix?
I also noticed some spray on the hood. Looks like something is getting on the belt, but there is also another large spot. Neither are wet, so i donít think it is an active leak, but iím a chef not a mechanic!

This is the best plug, far left side.

This is the one just to the right of it. There was oil on the wire when I pulled it out.

So I replaced the gasket. And the air intake hose (only because i broke the last one ) And the pcv valve for good measure. The old gasket didn’t look in terrible shape - I could see no obvious flaws or failures. There were signs of oil seepage into the spark plug housing, though. Installation went fine, cleaned the cover and such, use sealant where appropriate, even borrowed a torque wrench from the Advance and tightened the nuts in order according to the manual. The engine light even went off. For a bit...

Alas, nothing is better. The light is back on. There are no leaks from the exterior, but I did not remove the spark plugs to let any oil that may still be in the housing to drain. But if there is enough oil there to cause what’s happening, I have bigger problems.

It is a manual transmission, and power is severely lacking at low RPM, up until about 3200. It also seems to crap out at 4100 or so. I ran the gears to the end, thinking that might burn off any oil that got into the combustion chamber when i last removed the spark plugs. Even when cruising along at 73 mph(3300RPM), it will suddenly (but just so slightly) lose umph. If i press on the accelerator it will go back up and cruise at 75, but i don’t really wanna drive around that fast!

Should I change the plugs? I know it needs a new air filter, but even if one were to remove an air filter from a brand new car, it would not have these results.

well for starters, you need to take propane torch to those plugs. burn electrodes white hot. pliers of course to hold plug, don't repeat MY mistakes.
also, run a can of Seafom via fuel tank and another via engine oil for several hundred miles, then change oil. this will clean crud everywhere.
did you do just cover gasket or plug seals too? as that's where oil primarily leaks onto the plugs. light rubber donuts sealing plug tubes.
of course your engine sounds like having vacuum/air leaks all over.